Message-ID: <4041493F.44ACB36D@frontiernet.net>
Date: Sat, 28 Feb 2004 20:06:55 -0600
From: Jim Sower <canarder@frontiernet.net>
MIME-Version: 1.0
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: FW: [VAF Mailing List] Engine Choice
References: <list-3049779@logan.com>
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<... A wind milling prop DOES have hugh drag compared to a
stopped one ...>
I know a wind milling prop (prop turning engine) has more drag
than a stopped prop (frozen engine or not enough airspeed to
overcome engine compression).  This guy specified a freewheeling
prop (sprag clutch that is in the overrunning mode).  There is
no resistance at all to the prop and the only "work" the
slipstream has to do is overcome the negligible sprag clutch
free wheeling friction.  Contrast that with the force required
to overcome engine compression, or that required to try as hard
as it can to overcome compression and not quite be able to do
it.

I can't argue with your experience, but I had always understood
that a frozen prop had less drag than a prop wind milling the
engine, but that the difference was not significant.  A
freewheeling prop is waaaay different from a wind milling prop. 
Like if you have a sprag clutch and turn up the engine to high
rpm and then shut it down, the engine stops immediately but the
prop will keep spinning for a couple of minutes.

<... When you think wind milling drag ... think prop circle
area, not just the blades cross section themselves. Square yards
of drag, not square ft ...>
I don't think that's exactly the way it works quantitatively. 
Maybe Marc can help.  Oooops!  Marc is not on this list.

As I read it .... Jim S.